^yep, hold the gun so the bottle is on your forearm, then bend your arm toward you at 90 degree angle. if the back of the bottle meets the break of your arm, the marker is set correctyly for you.
try not tp get a dropforward. it rasies your gun position and youre more likely to get shot when shooting from behind a bunker.
and the ASA also lets you turn the air on and off instead of disconnecting the bottle - much easier